1. Field of the Invention
The present invention relates to a linear precision guide of the type comprising a rail and a ball bearing block.
2. Brief Description of the Background of the Invention Including Prior Art
Linear precision guides are known which comprise at least one circular section rail and a sliding bushing equipped with inner ball circuits enabling the transfer of said bushing. This type of guide permits large and small displacements. In the case of small displacements, the rail is fixed to supports at its extremities and the bushing is closed. In the case of large displacements requiring the abutment of several rails and the intermediary fixation of said rails by one or more supports, the bushing is open to allow the passage of the support or supports, although the abutment of rail sections is easily accomplished as the circular section makes it possible to carry out perfectly concentric boring operations designed to receive assembly pins. The guide is limited in load on account of the point contact of the balls with the rail and, furthermore, the circular rail section does not ensure retention during rotation which calls for the use of a second parallel rail to compensate for this drawback. For the open bushings, the load capacity is limited on account of their elasticity.
There are further known guides comprising a ballbearing bushing sliding on a triangular rail where each vertex is provided with grooves on both sides, in which grooves the balls of the bearing travel. This type of guide makes it possible to bear greater loads than the guides previously described due to the fact that the balls travel in the grooves and allow the transmission of couples and, as a result, to obtain a combined transfer/rotation movement. However, the displacements are limited to reduced lengths, given the fact that the rail can only be fixed at its extremities.
Linear guides are also known which comprise prismatic-section rails provided with at least one groove on each of their lateral faces serving as the race for movable balls maintained in the grooves disposed on either side of the inner jaws of the block and whose endless movement is obtained by a return corridor disposed in the said jaws, as described in the French Patent No. 2,546,995, 2,516,612, 2,545,557, 730,922, 2,302,446. This type of guide presents positive advantages, in particular at the contact level of the balls in the grooves, which allow to increase the load capacity, their reduced dimensions and their high strength on account of the direct fixation of the rail to the frame, the disposition of the balls on the lateral faces of the rail making it possible to support transverse couples. This type of guide has certain disadvantages and requires considerable rectification operations, on the one hand, for fixation to the frame, especially of those with two reference faces at 90 degrees, for the rail and for those of the support frame bearing the rail and, on the other hand, for realizing guides of larger lengths which call for the abutment of several rails. This operation to obtain a perfect alignment of said rails is delicate since it is almost impossible, as is the case with the triangular rail sections, to realize cylindrical boring operations at the extremities in a concentric manner so as to receive assembly pins, just as it is also impossible to combine transfer and rotation movements.
In all the previously described linear guides, the blocks or bushings are made up of a very large number of complex elements which burden its construction with costs.